The present invention relates to a new type of optical disk and a method for implementing the effects of the new device on existing optical disks, and in particular, to an optical disk with improved digital or analog signal reproduction from the optical disk coding by an optical reading assembly. Both the device and the method of the present invention extend to all forms of optical disk including, but not limited to prerecorded, recordable, rewriteable (magneto-optical) and other forms of optical disk.
Presently, optical disks consist of a layered structure 1 as shown in FIG. 1. In an optical disk player, laser light 2 from a laser diode is focused by the action of a series of lenses, and the transparent polycarbonate layer 3 itself, onto a reflective surface 4. The reflected light is then passed back into the optical system and separated, usually by a quarter-wave polarising plate or a half mirror, then detected by a series of photodiodes. By way of fast action servo systems, voltage levels from photodiodes control an objective lens to keep the focused region of the laser beam in alignment with the desired part of the optical disk.
The depth of the pits 5 is important for the operation of the disk. Pits are generally made a quarter of the laser light wavelength in depth. As the laser light is coherent and the reflected light from the region in-between the pits, defined as the land-region 6, travels an extra half wavelength compared to light from the reflective surface of the pits 4 which results in a degree of annihilation of the reflected light.
Thus, pit edges and surrounding land-regions are indicated by a low level of reflectance intensity, however, when the laser beam is focused on the reflective coating a strong reflective signal is obtained. This discrimination process leads to the reading of the information on an optical disk.
To further illustrate this, FIG. 2 shows laser light 2 from a light source positioned over a pit 5. Reflected laser light from near the pit edge at position 7 is a half-wavelength out of phase with reflected laser light from the position 8 if the depth of the pit 5 is a quarter of the wavelength of the laser light. Hence, reflected laser light from the periphery regions of a pit 5 and corresponding regions adjacent the pit, that is at the edge of land-regions 6, is low in intensity due to superpositioning of the 180xc2x0 out of phase reflected coherent laser light. It is these nulls in light intensity which are manifested as the information on the optical disk.
Digital optical disks may use a pit format which uses a master clock to identify information based on time-length. Normally, the master clock period is denoted T, then the smallest pit-length or land-length (that is the region between pits) is denoted 3T, then 4T, 5T, etc. The longest pit-length or land-length is denoted as 11T. These pit-lengths and land-lengths are a common element in present-day digital technology. Normally, the smallest pit-length period 3T is xe2x80x981xe2x80x99 in computer binary; 4T is xe2x80x9811xe2x80x99 in computer binary; and so on, they represent the positive waveform. The smallest land-length period 3T is xe2x80x980xe2x80x99 in computer binary; 4T is xe2x80x9800xe2x80x99; and so on, they represent the negative waveform. In a typical format, an analog waveform is completely represented by an eighteen digit word.
The protective film 9, shown in FIG. 1, is typically used to prevent damage to the pits which are in close proximity to the surface, and to allow a label to be imprinted onto the disk. The reflective information layer of some optical disk formats allow single-layer, dual-layer or multi-layer films on one side of disk. The analog tracks of an optical disk are recorded with small precise pits having variation in depth in the disk surface.
It is the variation in the intensity of reflected light which allows reproduction of the information contained within the disk as a configuration of pits to be reproduced electronically via the photodiodes. Inherent variations in reflection coefficients in the disk device can introduce undesirable noise levels, which if significant will result in misread or lost information.
Patent document U.S. Pat. No. 5,190,800 teaches of an optical recording medium having a substrate which contains a light absorbent capable of absorbing light other than the light used for recording and reproducing. This light filtering mechanism affects the overall transmittance of various wavelengths of light incident on the substrate but does not provide an enhanced means for edge (pit and land) identification in the optical recording medium. The document does not disclose a means for addressing the effects of reflected or refracted laser light inside the optical disk. Indeed, it is an object of this document to provide an optical recording medium which does not suffer from deterioration by ordinary light, rather than aid in the reproduction of signals by enhanced edge (pit and land) identification from the optical recording medium. Neither does the presence of a recording layer, light reflective layer or protective layer assist in this respect. These components are standard features of optical disks today and are not directed at assisting in edge (pit and land) identification at the recording and light reflective layers.
A brief outline of current optical disk technology, which is applicable to the present invention, follows. A recordable optical disk is typically structured as shown in FIG. 3. There is a thin exposed layer 10 and a reflecting layer 11. The reflecting layer 11 is positioned behind the exposed layer 10 and opposite the laser source. The reflecting layer 11 replaces the reflective surface 4 of FIG. 1. A short pulse of laser light is used to burn a spot on the exposed layer 10 when the material is in its amorphous state. These spots can create a xe2x80x98pitxe2x80x99 of a desired length.
Magneto-optical disks, also called erasable rewriteable-optical disks, are based on a hybrid of optical disk technology and magnetic disk technology. The thin exposed layer 10, of FIG. 3, is in this case a material which allows its magnetic state to be changed when heated to a certain temperature. Thus, this material replaces the thin exposed layer of a recordable laser disk. A low power laser is used to read the xe2x80x98pitsxe2x80x99 by detecting magnetic spots on the disk. The spots also keep the magnetic field direction they developed when heated. Another higher power laser is used to heat spots which thus change their magnetic state, hence making the xe2x80x98pitsxe2x80x99 erasable.
Hence, there are different formats of laser optical disk, the structures having different reflecting layers which may reflect a particular wavelength of the incident laser light. Modern lasers for optical disks often have automatic gain control circuits which help the opto-electronics read from the different reflecting layers. The basic format variations of the standard CDs family of optical disks include: Audio CD, CD-ROM, Video CD, CD-I, CD-R, CD-RW, Photo CD, CD-G, MovieCD, etc.
The detecting sensor (photodiode) is very important in laser optical technology. However, the photodiode does not detect what wavelength of light is reflected by the target. Additionally, the photodiode does not discriminate between light that is reflected or refracted by materials outside of the target, thus an ambiguous light signal may be obtained. This is the basis of a large proportion of errors being readout from the information on a disk.
Reduction of noise levels, that is a dither effect from pit reflection, induced by opto-electronics reading optical disks, and by the structure of the optical disks themselves, is an important issue. Besides improving the quality of sound and removing reading errors, improved identification of edge regions will allow a clear contrast between a pit-edge and a land-edge to be observed which may allow a higher density of digital information to be contained within an optical disk.
This identifies a need for an improved optical disk wherein higher reflected optical intensities and/or contrasts lead to both an improved tracking stability and significant noise reduction.
There is also a need to provide a method of achieving the effects of such an improved optical disk by applying the method to existing optical disks.
The present invention according to one aspect seeks to provide an improved optical disk device including:
an optical disk;
a first layer of material disposed upon at least a portion of the surface of the optical disk opposite to a laser source, the first layer of material able to substantially reflect laser light from the laser source;
a second layer of material(s) disposed over at least the first layer of material, the second layer of material(s) able to substantially absorb the laser light; and
a third layer of material disposed upon at least a portion of the surface of the optical disk adjacent to the laser source, the third layer of material able to substantially reflect laser light from the laser source.
In another preferred form of the invention it sought to provide that the first layer of material covers an area of the surface of the optical disk corresponding to at least the region of the optical disk used for pit encoding; and
the second layer of material(s) covers at least the first layer of material and the third layer of material.
The present invention according to another aspect seeks to provide that the third layer of material is excluded from the surface area of the optical disk required by the laser source to access the region of the optical disk containing the pit encoding.
The present invention according to yet another aspect seeks to provide that the second layer of material(s) is also disposed upon at least part of the lateral edges of the optical disk.
Preferably:
the first layer of material is substantially red in colour;
the second layer of material(s) is substantially green, blue or combinations thereof in colour(s);
the third layer of material is substantially red in colour.
In a broad form, the present invention provides that the layers of materials are embedded within the optical disk in regions or areas thus providing a similar effect as if the layers were disposed upon the surface of the optical disk.
In a further embodiment of the present invention there is provided a method of reducing errors when an opto-electronic system reads an optical disk, said method including the steps of:
depositing a first layer of material upon at least a portion of the surface of the optical disk opposite to a laser source, the first layer of material able to substantially reflect laser light from the laser source;
depositing a second layer of material(s) over at least the first layer of material, the second layer of material(s) able to substantially absorb the laser light; and
depositing a third layer of material upon at least a portion of the surface of the optical disk adjacent to the laser source, the third layer of material able to substantially reflect laser light from the laser source;
whereby the presence of the first, second and third layers of materials facilitates increased recognition of pit edges by the opto-electronic system than would otherwise be obtained if the layers of materials were not present.
In another preferred form of the invention there is provided a method wherein:
the first layer of material covers an area of the surface of the optical disk corresponding to at least the region of the optical disk used for pit encoding; and
the second layer of material(s) covers at least the first layer of material and the third layer of material.
In yet another preferred form of the invention there is provided a method wherein, the third layer of material is excluded from the surface area of the optical disk required by the laser source to access the region of the optical disk containing the pit encoding.
In still yet another preferred form of the invention there is provided a method wherein, the second layer of material(s) is also disposed upon at least part of the lateral edges of the optical disk.
Preferably, the present invention also provides a method wherein:
the first layer of material is substantially red in colour;
the second layer of material(s) is substantially green, blue or combinations thereof in colour(s);
the third layer of material is substantially red in colour.
Broadly, the present invention seeks to provide a method wherein, the layers of materials are embedded within the optical disk in regions or areas thus providing a similar effect as if the layers were disposed upon the surface of the optical disk.
Furthermore, the present invention seeks provide that the optical disk includes standard, pressed (pre-recorded), recordable, rewriteable (magneto-optical) or other forms of optical disk, and includes disk formats from the CD family of optical disks such as standard CD, Audio CD, CD-ROM, Video CD, CD-I, CD-R, CD-RW, Photo CD, CD-G, MovieCD and other related formats.
Improved optical disk device, substantially according to the embodiment described in the specification with reference to and as illustrated in the accompanying figures.
In yet a further broad form of the present invention, the present invention seeks to provide a method of reducing errors when an opto-electronic system reads an optical disk, substantially according to the embodiment described in the specification with reference to the accompanying figures.